Method for manufacturing an oxide superconducting article

ABSTRACT

A method for manufacturing a superconducting article, comprising the steps of: forming a first layer comprising a mixture of LnBa 2  Cu 3  O x  and Ln 2  BaCuO x  &#39; on the surface of a substrate, said Ln being an optional rare earth element; then forming a second layer comprising a mixture of at least CuO and BaCuO 2  on the surface of the first layer; and then melting the mixture in the second layer to cause the resultant melt of the mixture in the second layer to diffusion-react with Ln 2  BaCuO x  &#39; in the first layer so as to convert the first and second layers into a film of a superconducting substance comprising LnBa 2  Cu 3  O x  ; thereby manufacturing a superconducting article comprising the substrate and the film of the superconducting substance formed on the surface of the substrate.

This application is a continuation of application Ser. No. 07/482,203,filed Feb. 20, 1990 now abandoned.

REFERENCE TO PATENTS, APPLICATIONS AND PUBLICATIONS PERTINENT TO THEINVENTION

As far as we know, there is available the following prior art documentpertinent to the present invention:

"Japanese Journal of Applied Physics", Vol. 27, No. 8, pagesL1501-L1503, published on Jul. 22, 1988

The contents of the prior art disclosed in the above-mentioned prior artdocument will be discussed hereafter under the heading of the"BACKGROUND OF THE INVENTION".

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing asuperconducting article comprising a substrate and a film of asuperconducting substance formed on the surface of the substrate.

BACKGROUND OF THE INVENTION

Superconducting materials have already been practically applied in theform of a superconducting magnet in a particle accelerator, a medicaldiagnosing instrument and the like. Potential applications of thesuperconducting materials include, an electric power generator, anenergy storage device, a linear motor car, a magnetic separator, anuclear fusion reactor, a power transmission cable, and a magneticshielder. In addition, a superconducting element using the Josephsoneffect is expected to be applied in such fields as an ultra-high speedcomputer, an infrared sensor and a low-noise amplifier. The magnitude ofthe industrial and social impact which would be exerted the practicalrealization of these possible applications is really unmeasurable.

One of the typical superconducting materials so far developed is anNb-Ti alloy which is widely used at present as a magnetizing wire. TheNb-Ti alloy has a critical temperature, i.e., a critical temperaturefrom which a superconductive state occurs (hereinafter simply referredto as "Tc") of 9° K. As a superconducting material having a "Tc"considerably higher than that of the Nb-Ti alloy, a compound-typesuperconducting material has been developed, including an Nb₃ Sn (Tc:18° K.) and V₃ Ga (Tc: 15° K.) which are now practically employed in theform of a wire.

As a superconducting material having a "Tc" further higher than those ofthe above-mentioned alloy-type and compound-type superconductingmaterials, a composite oxide superconducting material containing aCu_(x) O_(y) -radical has recently been developed. For example, aY-Ba-Cu-O type superconducting material has a "Tc" of about 93° K. Sinceliquid nitrogen has a temperature of 77° K., liquid nitrogen availableat a lower cost than liquid helium can be used as a cooling medium forthe composite oxide superconducting material. Discovery of asuperconducting material having a high "Tc" applicable at a temperatureof liquid nitrogen urges further expectations for the foregoing fieldsof application. In the actual application, however, problems are how toprocess a superconducting material in the form of a film or a wire, andat the same time, how to increase a critical current density(hereinafter simply referred to as "Jc") of the superconductingmaterial.

In order to increase the "Jc" of a superconducting material, it isnecessary, when using the superconducting material in the form of afilm, to make the structure of the film dense with a singlesuperconducting phase.

A method for manufacturing a superconducting article, in which "Jc" of afilm of a superconducting material can be increased by making thestructure of the film of the superconducting material dense with asingle superconducting phase, is disclosed in the "Japanese Journal ofApplied Physics", Vol. 27, No. 8, pages L1501-L1503, published on Jul.22, 1988 (hereinafter referred to as the "prior art"). The prior art isdescribed below with reference to the drawings.

FIG. 1 is a schematic descriptive view illustrating the former halfsteps of the method of the prior art for manufacturing a superconductingarticle, and FIG. 2 is a schematic descriptive view illustrating thelatter half steps of the method of the prior art for manufacturing thesuperconducting article. First, a sheet-shaped substrate 1 comprising Y₂BaCuO_(x') is prepared. Then, a mixture of CuO and BaCO₃, in which theratio of copper (Cu) to barium (Ba) is Cu:Ba=5:3 in molar ratio, isprimary-fired at a temperature of 800° C. for 24 hours, cooled, andpulverized into a powder. The powder of the thus primary-fired mixtureis then secondary-fired at a temperature of 900° C. for 24 hours,cooled, and pulverized into a powder to prepare a powdery material for afilm. Subsequently, the thus prepared powdery material for a film ismixed with ethyl alcohol to prepare a slurry for a film.

Then, the thus prepared slurry for film is applied onto the surface ofthe substrate 1, and dried to form a film 2 comprising Ba-Cu oxides onthe surface of the substrate 1, as shown in FIG. 1. Then, the substrate1, on the surface of which the film 2 has thus been formed, is heated inan electric furnace to melt the film 2 to cause the resultant melt ofthe Ba-Cu oxides in the film 2 to diffusion-react with Y₂ BaCuO_(x') inthe substrate 1, thereby converting the film 2 into a film 3 of asuperconducting substance comprising YBa₂ Cu₃ O_(x), as shown in FIG. 2.

Then, the film 3 of the superconducting substance thus produced iscooled to a room temperature, thereby manufacturing a superconductingarticle comprising the non-reacting substrate 1 and the film 3 of thesuperconducting substance formed on the surface of the nonreactingsubstrate 1, as shown in FIG. 2.

The above-mentioned prior art has the following effects: Since the film3 of the superconducting substance comprising YBa₂ Cu₃ O_(x) is producedthrough the diffusion-reaction of the resultant melt of the Ba-Cu oxidesin the film 2 with Y₂ BaCuO_(x') in the substrate 1, the structure ofthe film 3 of the superconducting substance is dense with a singlesuperconducting phase, thus permitting manufacture of a superconductingarticle having a high "Jc".

However, the above-mentioned prior art has the following problem: Whenthe film 3 of the superconducting substance comprising YBa₂ Cu₃ O_(x) isproduced on the surface of the substrate 1 through thediffusion-reaction of the resultant melt of the Ba-Cu oxides in the film2 with Y₂ BaCuO_(x') in the substrate 1, the film 3 of thesuperconducting substance expands in volume, causing cracks in the film3 of the superconducting substance and resulting in seriouslydeteriorated superconducting properties of the superconducting articleincluding a largely decreased "Jc".

The above-mentioned problem occurs also in the case where the film 3 ofa superconducting substance is produced by means of a compoundcontaining an optional rare earth element other than "yttrium" (Y) inthe above-mentioned Y₂ BaCuO_(x') and YBa₂ Cu₃ O_(x). Such an optionalrare earth element is hereinafter represented by "Ln".

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a method formanufacturing a superconducting article, which permits prevention, whenproducing a film of a superconducting substance comprising LnBa₂ Cu₃O_(x) on the surface of a substrate through the diffusion-reaction, ofthe occurrence of cracks in the film of the superconducting substance,and as a result allows the manufacture of a superconducting articlehaving excellent superconducting properties.

In accordance with one of the features of the present invention, thereis provided a method for manufacturing a superconducting article,characterized by comprising the steps of:

forming a first layer comprising a mixture of Ln₂ BaCuO_(x') and Ln₂BaCuO_(x) on the surface of a substrate, said Ln being an optional rareearth element, and the content ratio of Ln₂ BaCuO_(x') in said firstlayer being within the range of from 5 to 80 wt. % relative to the totalamount of LnBa₂ Cu₃ O_(x) and Ln₂ BaCuO_(x') then

forming a second layer comprising a mixture of at least CuO and BaCuO₂on the surface of said first layer, said second layer having a meltingpoint within the range of from 800° to 1,000° C.; then

melting said mixure in said second layer, and keeping the molten stateof said second layer for a period of time of from 1 minute to 4 hours inan oxygen-containing atmosphere to cause the resultant melt of saidmixture in said second layer to diffusion-react with Ln₂ BaCuO_(x') insaid first layer, thereby converting said first layer and said secondlayer into a film of a superconducting substance comprising LnBa₂ Cu₃O_(x) ; and

cooling said film of said superconducting substance thus produced to aroom temperature, thereby manufacturing a superconducting articlecomprising said substrate and said film of said superconductingsubstance formed on the surface of said substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the former half steps inthe method of the prior art for manufacturing a superconducting article;

FIG. 2 is a cross-sectional view illustrating the latter half steps inthe method of the prior art for manufacturing a superconducting article;

FIG. 3 is a cross-sectional view illustrating the former half steps inan embodiment of the method of the present invention for manufacturing asuperconducting article;

FIG. 4 is a cross-sectional view illustrating the middle half steps inthe embodiment of the method of the present invention for manufacturinga superconducting article; and

FIG. 5 is a cross-sectional view illustrating the latter half steps inthe embodiment of the method of the present invention for manufacturinga superconducting article.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

From the above-mentioned point of view, extensive studies were carriedout to develop a method for manufacturing a superconducting article,which permits prevention, when producing a film of a superconductingsubstance comprising LnBa₂ Cu₃ O_(x) on the surface of a substratethrough the diffusion-reaction, of the occurrence of cracks in the filmof the superconducting substance, and as a result allows the manufactureof the superconducting article having excellent superconductingproperties.

As a result, the following finding was obtained: Cracks occur in thefilm of the superconducting substance comprising LnBa₂ Cu₃ O_(x) becausethe film of the superconducting substance expands in volume when thefilm of the superconducting substance comprising LnBa₂ Cu₃ O_(x) isproduced on the surface of the substrate through the diffusion reaction.Cracks can therefore be prevented from occurring in the film of thesuperconducting substance comprising LnBa₂ Cu₃ O_(x), by reducing theamount of LnBa₂ Cu₃ O_(x) produced through the diffusion reaction toreduce the amount of expansion in volume of the film of thesuperconducting substance comprising LnBa₂ Cu₃ O_(x).

The present invention was developed on the basis of the above-mentionedfinding. Now, an embodiment of the method of the present invention formanufacturing a superconducting article is described below withreference to the drawings.

FIG. 3 is a schematic descriptive view illustrating the former halfsteps in an embodiment of the method of the present invention formanufacturing a superconducting article; FIG. 4 is a schematicdescriptive view illustrating the middle half steps in the embodiment ofthe method of the present invention for manufacturing a superconductingarticle; and FIG. 5 is a schematic descriptive view illustrating thelatter half steps in the embodiment of the method of the presentinvention for manufacturing a superconducting article.

In the method of the present invention for manufacturing asuperconducting article, a first layer 5 comprising a mixture of LnBa₂Cu₃ O_(x) and Ln₂ BaCuO_(x') is first formed by means of the knownplasma metallizing method or the like on the surface of a substrate 4 asshown in FIG. 3. The substrate 4 comprises any one of ceramics, nickeland nickel-based alloy, which hardly reacts with a superconductingsubstance comprising LnBa₂ Cu₃ O_(x). The content ratio of Ln₂BaCuO_(x') in the first layer 5 should be within the range of from 5 to80 wt. % relative to the total amount of LnBa₂ Cu₃ O_(x) and Ln₂BaCuO_(x').

The content ratio of Ln₂ BaCuO_(x') in the first layer 5 is limitedwithin the above-mentioned range for the following reason: With acontent ratio of Ln₂ BaCuO_(x') of under 5 wt. %, the amount of Ln₂BaCuO_(x') in the first layer 5 is insufficient relative to the amountof a mixture in a second layer described later, so that the non-reactingfraction of the mixture in the second layer remains in a film describedlater of the superconducting substance comprising LnBa₂ Cu₃ O_(x), whichfilm is to be formed on the surface of the substrate 4, thus causingdeterioration of superconducting properties of the film of thesuperconducting substance. With a content ratio of Ln₂ BaCuO_(x') ofover 80 wt. %, on the other hand, the excessive amount of Ln₂ BaCuO_(x')makes it impossible to prevent cracks from occurring in the film of thesuperconducting substance comprising LnBa₂ Cu₃ O_(x), which cracks arecaused by the expansion in volume of the film during formation of thefilm.

Then, as shown in FIG. 4, a second layer 6 having a melting point withinthe range of from 800° to 1,000° C. is formed by means of the knownplasma metallizing method on the surface of the first layer 5. Thesecond layer 6 comprises a mixture of at least CuO and BaCuO₂. A typicalsecond layer 6 comprises a mixture of CuO, BaCuO₂ and BaO. In this case,the ratio of copper (Cu) to barium (Ba) in the second layer 6 should bewithin the range of Cu:Ba=1:0.10 to 0.95 in molar ratio. Another exampleof the second layer 6 comprises a mixture of CuO, BaCuO₂, BaO, Y₂ O₃ andYBa₂ Cu₃ O₇. In this case, the ratio of copper (Cu) to barium (Ba) andyttrium (Y) in the second layer 6 should be within the range ofCu:Ba:Y=1:0.10 to 0.95:0.001 to 0.330 in molar ratio. Any of thesemixtures in the second layer 6 diffusion-reacts with Ln₂ BaCuO_(x') inthe first layer 5, and, as a result, the first layer 5 and the secondlayer 6 are converted into a film of a superconducting substancecomprising LnBa₂ Cu₃ O_(x), as described below.

Then, the second layer 6 is melted, and the molten state of the secondlayer 6 is kept for a period of time of from 1 minute to 4 hours in anoxygen-containing atmosphere to cause the resultant melt of the mixturecomprising at least CuO and BaCuO₂ in the second layer 6 todiffusion-react with Ln₂ BaCuO_(x') in the first layer 5, therebyconverting the first layer 5 and the second layer 6 into a film 7 of asuperconducting substance comprising LnBa₂ Cu₃ O_(x), as shown in FIG.5.

The period of time of keeping the molten state of the second layer 6 islimited within the range of from 1 minute to 4 hours for the followingreason: With a period of time of molten state of the second layer 6 ofunder 1 minute, the resultant melt of the mixture in the second layer 6cannot be caused to sufficiently diffusion-react with Ln₂ BaCuO_(x') inthe first layer 5. With a period of time of molten state of the secondlayer 6 of over 4 hours, on the other hand, conversion of the firstlayer 5 and the second layer 6 into the film 7 of the superconductingsubstance comprising LnBa₂ Cu₃ O_(x) does not proceed further.

The thus produced film 7 of the superconducting substance is then cooledto a room temperature, thereby manufacturing a superconducting articlecomprising, as shown in FIG. 5, the substrate 4 and the film 7 of thesuperconducting substance formed on the surface of the substrate 4.

According to the method of the present invention for manufacturing asuperconducting article, as described above, the first layer 5previously contains LnBa₂ Cu₃ O_(x) in a prescribed amount, and thisreduces the amount of LnBa₂ Cu₃ O_(x) produced through thediffusion-reaction of the melt of the mixture in the second layer 6 withLn₂ BaCuO_(x') in the first layer 5. As a result, the amount ofexpansion in volume of the film 7 of the superconducting substancecomprising LnBa₂ Cu₃ O_(x) is reduced, thus preventing cracks fromoccurring in the film 7 of the superconducting substance.

Now, the method of the present invention for manufacturing asuperconducting article is described in more detail by means of exampleswith reference to FIGS. 3 to 5.

EXAMPLE 1

A mixture of CuO, BaCO₃ and Y₂ O₃, in which the ratio of copper (Cu) tobarium (Ba) and yttrium (Y) was Cu:Ba:Y=2:1.5:1.5 in molar ratio, wasprimary-fired at a temperature of 900° C. for 10 hours, cooled andpulverized into a powder. The powder of the thus primary-fired mixturewas then secondary-fired at a temperature of 920° C. for 10 hours,cooled and pulverized into a powder. The powder of the thussecondary-fired mixture was then tertiary-fired at a temperature of 950°C. for 10 hours, cooled and pulverized into a powder to prepare apowdery material for first layer, having an average particle size withinthe range of from 26 to 44 μm. The thus prepared powdery material forthe first layer comprised a mixture of YBa₂ Cu₃ O_(x) and Y₂ BaCuO_(x')and the content ratio of Y₂ BaCuO_(x') in the powdery material for firstlayer was 50 wt. % relative to the total amount of YBa₂ Cu₃ O_(x) and Y₂BaCuO_(x').

On the other hand, a mixture of CuO and BaCO₃, in which the ratio ofcopper (Cu) to barium (Ba) was Cu:Ba=2:1 in molar ratio, wasprimary-fired at a temperature of 900° C. for 10 hours, cooled andpulverized into a powder. The powder of the thus primary-fired mixturewas then secondary-fired at a temperature of 920° C. for 10 hours,cooled and pulverized into a powder. The powder of the thussecondary-fired mixture was then tertiary-fired at a temperature of 950°C. for 30 minutes, cooled and pulverized into a powder to prepare apowdery material for second layer, having an average particle sizewithin the range of from 26 to 44 μm. The thus prepared powdery materialfor second layer comprised a mixture of CuO, BaCuO₂ and BaO.

Then, the powdery material for first layer prepared as described abovewas blown by means of the known plasma metallizing method onto thesurface of a substrate 4 having a surface area of 1 cm² and a thicknessof 1 mm and comprising a nickel-based alloy, to form a first layer 5having a thickness of 50 μm on the surface of the substrate 4, as shownin FIG. 3.

Then, the powdery material for second layer prepared as described abovewas blown by means of the known plasma metallizing method onto thesurface of the first layer 5, to form a second layer 6 having athickness of 50 μm on the surface of the first layer 5, as shown in FIG.4.

Then, the substrate 4, on the surface of which the first layer 5 and thesecond layer 6 were thus formed, was heated to a temperature of 950° C.in an electric furnace having an interior atmosphere of air to melt thesecond layer 6, and the molten state of the second layer 6 was kept for30 minutes. This permitted the diffusion reaction of the resultant meltof the mixture of CuO, BaCuO₂ and BaO in the second layer 6 with Y₂BaCuO_(x') in the first layer 5, whereby the first layer 5 and thesecond layer 6 were converted into a film 7 of a superconductingsubstance comprising YBa₂ Cu₃ O_(x) having a thickness of 70 μm, asshown in FIG. 5.

The substrate 4, on the surface of which the film 7 of thesuperconducting substance was thus produced, was slowly cooled in theelectric furnace to a room temperature.

Thus, a superconducting article was manufactured, which comprised thesubstrate 4 comprising a nickel-based alloy and the film 7 of thesuperconducting substance comprising YBa₂ Cu₃ O_(x) formed on thesurface of the substrate 4, as shown in FIG. 5.

Investigation of the thus manufactured superconducting article revealedthat the structure of the film 7 was dense with a single superconductingphase, and the superconducting article had a "Jc" of 1,000 A/cm².

EXAMPLE 2

A mixture of CuO, BaCO₃ and Y₂ O₃, in which the ratio of copper (Cu) tobarium (Ba) and yttrium (Y) was Cu:Ba:Y=2.4:1.7:1.3 in molar ratio, wasprimary-fired at a temperature of 900° C. for 10 hours, cooled andpulverized into a powder. The powder of the thus primary-fired mixturewas then secondary-fired at a temperature of 920° C. for 10 hours,cooled and pulverized into a powder. The powder of the thussecondary-fired mixture was then tertiary-fired at a temperature of 950°C. for 10 hours, cooled and pulverized into a powder to prepare apowdery material for first layer, having an average particle size withinthe range of from 26 to 44 μm. The thus prepared powdery material forfirst layer comprised a mixture of YBa₂ Cu₃ O_(x) and Y₂ BaCuO_(x') andthe content ratio of Y₂ BaCuO_(x') in the powdery material for firstlayer was 30 wt. % relative to the total amount of YBa₂ Cu₃ O_(x) and Y₂BaCuO_(x').

On the other hand, a mixture of CuO, BaCO₃ and Y₂ O₃, in which the ratioof copper (Cu) to barium (Ba) and yttrium (Y) was Cu:Ba:Y=26:13:1 inmolar ratio, was primary-fired at a temperature of 900° C. for 10 hours,cooled and pulverized into a powder. The powder of the thusprimary-fired mixture was then secondary-fired at a temperature of 920°C. for 10 hours, cooled and pulverized into a powder. The powder of thethus secondary-fired mixture was then tertiary-fired at a temperature of950° C. for 30 minutes, cooled and pulverized into a powder to prepare apowdery material for second layer, having an average particle sizewithin the range of from 26 to 44 μm. The thus prepared powdery materialfor second layer comprised a mixture of CuO, BaCuO₂, BaO, Y₂ O₃ and YBa₂Cu₃ O₇.

Then, the powdery material for first layer prepared as described abovewas blown by means of the known plasma metallizing method onto thesurface of a substrate 4 having a surface area of 1 cm² and a thicknessof 1 mm and comprising a nickel-based alloy, to form a first layer 5having a thickness of 50 μm on the surface of the substrate 4, as shownin FIG. 3.

Then, the powdery material for second layer prepared as described abovewas blown by means of the known plasma metallizing method onto thesurface of the first layer 5, to form a second layer 6 having athickness of 50 μm on the surface of the first layer 5, as shown in FIG.4.

Then, the substrate 4, on the surface of which the first layer 5 and thesecond layer 6 were thus formed, was heated to a temperature of 950° C.in an electric furnace having an interior atmosphere of air to melt thesecond layer 6, and the molten state of the second layer 6 was kept for30 minutes. This permitted the diffusion reaction of the resultant meltof the mixture of CuO, BaCuO₂, BaO, Y₂ O₃ and YBa₂ Cu₃ O₇ in the secondlayer 6 with Y₂ BaCuO_(x') in the first layer 5, whereby the first layer5 and the second layer 6 were converted into a film 7 of asuperconducting substance comprising YBa₂ Cu₃ O_(x) having a thicknessof 70 μm, as shown in FIG. 5.

Then, the substrate 4, on the surface of which the film 7 of thesuperconducting substance was thus produced, was slowly cooled in theelectric furnace to a room temperature.

Thus, a superconducting article was manufactured, which comprised thesubstrate 4 comprising a nickel-based alloy and the film 7 of thesuperconducting substance comprising YBa₂ Cu₃ O_(x) formed on thesurface of the substrate 4, as shown in FIG. 5.

Investigation of the thus manufactured superconducting article revealedthat the structure of the film 7 was dense with a single superconductingphase, and the superconducting article had a "Jc" of 1,100 A/cm².

According to the method of the present invention, as described above indetail, it is possible to manufacture a superconducting article havingexcellent superconducting properties, in which cracks are prevented fromoccurring in a film of a superconducting substance comprising LnBa₂ Cu₃O_(x), when the film of the superconducting substance is produced on thesurface of a substrate through the diffusion-reaction, thus providingindustrially useful effects.

What is claimed is:
 1. A method for manufacturing a superconducting article, comprising the steps of:forming a first layer comprising a mixture of a superconductor LnBa₂ Cu₃ O_(x) and a Ln₂ BaCu oxide on a surface of a substrate selected from the group consisting of ceramics, nickel and a nickel alloy, said Ln is a rare earth element, said mixture of the superconductor LnBa₂ Cu₃ O_(x) and the Ln₂ BaCu oxide being prepared by subjecting a mixture of CuO, BaCO₃ and Ln₂ O₃ to a plurality of treatments, each comprising a firing, a cooling and a pulverizing, and the content ratio of the Ln₂ BaCu oxide in said first layer being within the range of from 5 to 80 wt. % relative to the total amount of the superconductor LnBa₂ Cu₃ O_(x) and the Ln₂ BaCu oxide; then forming a second layer comprising a mixture of at least CuO and BaCuO₂ on a surface of said first layer, the molar ratio of copper to barium in said second layer being within the range of copper: barium=1:0.10 to 0.95, and said second layer having a melting point of from 800° to 1,000° C.; then melting said mixture in said second layer, and keeping the molten state of said second layer for a period of time of from 1 minute to 4 hours in an oxygen-containing atmosphere to cause the resultant melt of said mixture in said second layer to diffusion-react with the Ln₂ BaCu oxide in said first layer, thereby converting said first layer and said second layer into a film of an oxide superconductor comprising the superconductor LnBa₂ Cu₃ O_(x) ; and cooling said film of said oxide superconductor thus produced to room temperature, thereby manufacturing said superconducting article comprising said substrate and said film of said oxide superconductor formed on the surface of said substrate.
 2. The method as claimed in claim 1, wherein:said second layer comprises a mixture of CuO, BaCuO₂ and BaO.
 3. The method as claimed in claim 1, wherein:said second layer comprises a mixture of CuO, BaCuO₂, BaO, Y₂ O₃ and YBa₂ Cu₃ O₇ ; and the ratio of copper (Cu) to barium (Ba) and yttrium (Y) in said second layer is within the range of Cu:Ba:Y=1:0.10 to 0.95:0.001 to 0.330 in molar ratio.
 4. The method of claim 1, wherein the first layer comprises a mixture of a superconductor YBa₂ Cu₃ O_(x) and a Y₂ BaCu oxide with a content of the Y₂ BaCu oxide of 50 wt. % relative to the total amount of the superconductor YBa₂ Cu₃ O_(x) and the Y₂ BaCu oxide, the second layer comprises a mixture of CuO, BaCuO₂ and BaO, with a molar ratio of copper to barium of 2:1 and the substrate comprises a nickel alloy.
 5. The method of claim 1, wherein the first layer comprises a mixture of a superconductor YBa₂ Cu₃ O_(x) and a Y₂ BaCu oxide with a content of the Y₂ BaCu oxide of 30 wt. % relative to the total amount of the superconductor YBa₂ Cu₃ O_(x) and the Y₂ BaCu oxide, the second layer comprises a mixture of CuO, BaCuO₂, BaO, Y₂ O₃ and YBa₂ Cu₃ O₇, with a molar ratio of copper to barium to yttrium of 26:13:1 and the substrate comprises a nickel alloy.
 6. The method of claim 1, wherein the first layer is formed by a plasma metallizing method on the substrate.
 7. The method of claim 6, wherein the second layer is formed by a plasma metallizing method on the first layer.
 8. The method of claim 1, wherein Ln is Y.
 9. The method of claim 8, wherein the substrate is a ceramic.
 10. The method of claim 8, wherein the substrate is nickel.
 11. The method of claim 8, wherein the substrate is a nickel alloy. 